1. Field of the Invention
The present invention relates to novel organic phosphorus compounds of non-halogen type and flame-retarded resin compositions containing the same which are excellent in flame-retardant properties and heat resistance.
2. Description of the Related Art
Organic polymers such as thermoplastic resins (e.g., polypropylene, polystyrene and acrylonitrile-butadienestyrene (ABS) resins) and thermosetting resins (e.g., polyurethane and phenol resins) are available at relatively low cost and have excellent properties such as easy molding. Such organic polymers are widely used in all kinds of commodities including electronic components and automobile components. However, these organic polymers are flammable. Once they are involved in fire, they are readily burned and lost. A fire of cable causes great damage to our society. A law has recently been enacted which provides that these organic polymers shall be flame-retardant when used in products for daily use such as electric products, automobile interior decoration components and fiber products. For example, in the United States, there are the UL standards for electric apparatus and MVSS-302 Flame-Retardant Rule for automobiles.
As a known method for giving flame-retardant properties to organic polymers, a flame-retardant is added to organic polymers when preparing a molded product. As the flame-retardants, there are inorganic compounds, organic phosphorus compounds, organic halogen compounds and organic phosphorus compounds containing halogen. Of the above compounds, organic halogen compounds and organic phosphorus compounds containing halogen exhibit excellent flame-retardant effect. However, these compounds containing halogen are pyrolyzed in the process of molding resins and produce hydrogen halide, which corrodes molds and causes resins to be deteriorated and colored. Furthermore, such compounds adversely affect our working environment. Still furthermore, the compounds generate toxic gas, such as hydrogen halide, which is toxic to human bodies.
Typical flame-retardants which do not contain halogens are inorganic compounds such as magnesium hydroxide. However, since these inorganic compounds are inferior in flame-retardant effect, it is necessary to add a large amount to achieve sufficient flame-retardant effect. Thus such flame-retardants have a drawback of allowing resins to be deprived of their inherent properties.
Halogen-free organic phosphorus compounds are generally used as flame-retardant having a relatively favorable flame-retardant effect. Aromatic phosphorus compounds such as triphenyl phosphate (TPP), tricresyl phosphate (TCP) and cresyl diphenylphosphate (CDP), which are typical organic phosphorus compounds, are used as flame retardants for each kind of engineering plastics, such as phenol resin, epoxy resin and polyurethane resin or the like.
However, triphenyl phosphate can hardly give flame-retardant properties to resins because it contains phosphorus at a low ratio. Triphenyl phosphate is usually used together with a halogen type flame-retardant. Furthermore, when triphenyl phosphate is singly used, it must be used in large amounts. This will impair various physical properties of resins and readily cause resins to be colored and deteriorated.
In addition, German Patent No. 3004184C2 discloses compounds of formula (A) as a flame-retardant which is added to an organic polymer such as polyolefin, polypropylene, polystyrene, ABS and polyurethane. ##STR2##
However, one of the main disadvantages of using these compounds lies in that a large amount thereof needs to be added to an organic polymer to give sufficient flame-retardant properties to resins because these compounds contain phosphorus at a low ratio, thereby resulting in inferior physical properties of resins. It is further noted that when R'.sub.1 to R'.sub.5 in the above formula (A) are methyl groups, the compounds have a low heat resistance, which leads to a disadvantage of causing resins to be colored and deteriorated in the process of molding.
In recent years, the development of plastics having high functional properties, such as engineering plastics and super-engineering plastics are in progress. Since these plastics need a high molding temperature, a flame-retardant is also required to be sufficiently heat resistant. As a known method for improving the heat resistance of flame-retardants, an anti-oxidant such as hindered-phenol compounds, sulfur compounds and amine compounds together with flame-retardant is added to organic polymers. However, even when such anti-oxidants are added to organic polymers, for example, together with the organic phosphorus compounds as mentioned above, coloring of resins cannot be avoided at 200.degree. C. or more.